One good exampel is Apple. They were a computer company which was doing well again after the return of Jobs. Then came the iPod. And revenue exploded. But when the rumors of a phone appeared, a lot of people would comment: no, they won't do that as that would eat into their cash cow iPod. But we know how this ended. They released the iPhone, grew multiple times the size the company was and eventually even stopped making iPods.

Back to Kodak: they did invent the digital camera, but at a time it was way too early for being a product. But more importantly, they did bring some important digital cameras to the market in the late 90ies, the first usuable DSLR were Nikon/Canon cameras equipped with Kodak guts. They started the professional digital camera market. Without Kodak, it might have happened years later.

And at that moment, when the writing for film was clearly on the wall and they actually had managed to kick start its killer, they dropped the ball. Good management would have seen that they could "protect" film sales only on a per-quarter basis, but it was a dying business. They should have used the billions of cash they still had, to gain a solid foothold in the digital camera business, perhaps even outright bought Nikon, which was limping for a while.

Or invest strongly in all the adjacencies of digital imaging, which they did far too late.

I think you can find examples of failed pivots and successful pivots but I'm not sure that "big companies should stick with their current cash cow and never pivot" is a best practice.

Any yes, people are all over it to the point that the most popular varieties can be difficult to find in stock, and prices have climbed significantly from a few years ago.